Conventionally, a light-emitting device using a light-emitting element such as a light-emitting diode (LED) has been widely used. FIG. 3 to FIG. 5 each depict an example of structure of a light-emitting device of an old type. In manufacture of the light-emitting device depicted in FIG. 3, an LED element 33 is bonded onto a substrate 31 with a die bond adhesive 32, and a p electrode 34 and an n electrode 35 on an upper surface of the LED element 33 are wire-bonded to the substrate 31 with gold (Au) wires 37 by silver plating 36. With this, the LED element 33 and the substrate 31 are electrically bonded together. Normally, the whole LED element 33 is sealed with a resin such as a transparent mold resin (not shown). In some cases, exfoliation may occur at a connecting portion of any of the gold wires 37 due to a difference in coefficient of linear expansion between the resin, and the LED element 33 and the gold wires 37, and an electric connection defect may occur due to a break of any of the gold wires 37.
In general, for this light-emitting device, it is desired to inhibit a decrease in reflectance of light emitted from the LED element and maintain luminous efficiency (light extraction efficiency). In the light-emitting device depicted in FIG. 3, metal electrodes are normally used as the p electrode 34 and the n electrode 35 of the LED element 33. However, among light beams emitted from the LED element 33, a light beam having a wavelength of 400 nm to 500 nm emitted to an upper surface side is absorbed into the gold electrodes and the gold wires, and a light beam emitted to a lower side is absorbed into the die bond adhesive 32. This light absorption decreases luminous efficiency (light extraction efficiency) of the LED element 33. Moreover, the adhesion process with the die bond adhesive 32 is based on oven curing, thereby disadvantageously taking time for manufacture.
In the light-emitting device depicted in FIG. 4, a conductive paste 37 typified by a silver paste is used. With this conductive paste 37, the p electrode 34 and the n electrode 35 on the lower surface of the LED element 33 and the silver-plated portion 36 on the substrate 31 are electrically bonded together. However, since the conductive paste 37 has a weak adhesion force, reinforcement by a sealing resin 38 is required. Furthermore, light may be diffused or absorbed inside the conductive paste 37, thereby decreasing luminous efficiency of the LED element 33.
Thus, for example, what is suggested is electrical bonding in which an anisotropic conductive adhesive (ACP) or an anisotropic conductive adhesive film (ACP) is cured to connect and fix the LED element and the substrate together. For example, Patent Document 1 describes a method of flip-chip mounting the LED element. Also, for example, in the light-emitting device depicted in FIG. 5, a commercially-available anisotropic conductive adhesive 39 is used to electrically bond the p electrode 34 and the n electrode 35 on the lower surface of the LED element 33 and the substrate 31 together by flip-chip mounting. In this flip-chip mount technology, a bump 40 is formed on each of the p electrode 34 and the n electrode 35.
In the technology of Patent Document 1, a light reflective layer such as a metallized layer is provided to the LED element so as to be insulated from the p electrode and the n electrode. With this, a decrease in reflectance of light emitted from the LED element is inhibited to maintain luminous efficiency. However, this technology of Patent Document 1 has disadvantages such that the number of manufacturing processes of the light-emitting device is increased and cost is inevitably increased. On the other hand, in the light-emitting device depicted in FIG. 5, while a light reflective layer is not provided, Au or Ni to be used as conductive particles dispersed in an ACP binder appears brown or dark brown, and an imidazole-based latent curing agent normally contained in the binder appears brown. For such reasons, the ACP binder appears brown as a whole, thereby absorbing light. As a result, luminous efficiency of the LED element 33 is decreased.
Patent Document
PTL 1: Japanese Patent Application Laid-Open No. 11-168235
Meanwhile, an epoxy resin is used as a binder resin in the ACP. In the ACP using the epoxy resin, an increase in conduction resistance, exfoliation of an adhesion surface, a crack, and others occur due to an internal stress based on a difference in coefficient of thermal expansion with temperature changes with respect to a connection substrate. For this reason, reliability may be decreased regarding corresponding reflow of lead-free solder, resistance to thermal shock, resistance to a corrosion phenomenon of a vapor-deposited wiring when used and stored in an atmosphere at high temperature and high humidity, and others.